1. Field of the Invention
The present invention relates to a writing apparatus and a writing method, and more particularly to an apparatus and a method for writing complementary patterns used for double patterning or double exposure.
2. Description of Related Art
The lithography technology which promotes micro-miniaturization of semiconductor devices is extremely important as being the only process whereby patterns are formed in the semiconductor manufacturing. In recent years, with the high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. Then, in order to form a desired circuit pattern on such semiconductor devices, there is a need for a highly accurate master or “original” pattern (also called a mask or a reticle).
Therefore, with the miniaturization of the circuit critical dimension, an exposure light source having a shorter wavelength is required. As a method for extending the life of an ArF laser, which is an example of the exposure light source, a double exposure technique and a double patterning technique attract attention in recent years. The double exposure is a method of continuously exposing the same region on a resist coated wafer while exchanging two masks. (For example, refer to Patent Literature 1.) Then, through developing and etching processes, a desired pattern is formed on the wafer. On the other hand, the double patterning is a method of exposing a resist coated wafer by using the first mask, and after developing and etching processes, the wafer is coated with resist again so that the same region thereof may be exposed using the second mask. These techniques have an advantage in that they can be performed as an extension of the current technique. In these techniques, two masks are necessary for obtaining a desired pattern on the wafer.
FIG. 8 is a schematic diagram showing masks used for the double patterning. In order to expose a desired pattern 302 onto the wafer, since sufficient resolution cannot be obtained by using a photomask 300, the mask needs to be divided into two as shown in FIG. 8. That is, a pattern 312 being a part of the pattern 302 is formed on a photomask 310, and a pattern 314 being the residual part of the pattern 302 is formed on a photomask 320. Then, the two photomasks 310 and 320 are set in order in an exposure apparatus, such as a stepper and a scanner, to be exposed respectively.
These photomasks are manufactured using an electron beam writing apparatus. Since the electron beam writing technique intrinsically has excellent resolution, it is used for producing highly precise master patterns.
FIG. 9 is a schematic diagram showing operations of a variable-shaped type electron beam (EB) writing apparatus. The variable-shaped type electron beam writing apparatus operates as follows: A first aperture plate 410 has a quadrangular, such as a rectangular opening or “hole” 411 for shaping an electron beam 330. A second aperture plate 420 has a variable-shaped opening 421 for shaping the electron beam 330 that has passed through the opening 411 into a desired rectangular shape. The electron beam 330, emitted from a charged particle source 430 and having passed through the opening 411, is deflected by a deflector so as to pass through a part of the variable-shaped opening 421 and thereby to irradiate a target workpiece or “sample” mounted on a stage. The stage continuously moves in one predetermined direction (e.g. X direction) during writing or “drawing”. In other words, a rectangular shape as a result of passing through both the opening 411 and the variable-shaped opening 421 is written in the writing region of a target workpiece 340 on the stage. This method of forming a given shape by letting beams pass through both the opening 411 and the variable-shaped opening 421 is referred to as a variable shaped method.
As described above, through the operations of the electron beam writing apparatus, a plurality of photomasks for the double exposure or for the double patterning exposure is manufactured. Then, when writing using the electron beam pattern writing apparatus, drift of the electron beam occurs as a temporal change. As a result, there is a problem that a positional deviation occurs between positions in writing the first mask and the second mask which are complementarily related, even when writing at a desired position. In the case of the positional deviation, consequently, a superposition error (overlay error) of the patterns occurs. For example, there is a problem that adjacent patterns which are to be separated from each other keeping a predetermined distance therebetween contact each other to cause a short circuit.
In the mask manufacturing process, as mentioned above, there is a problem that an error caused by drift of electron beams occurs between writing positions of complementary mask patterns. Therefore, there exists a problem in that a superposition error between patterns is induced when exposing using these two masks.